This invention relates to light emitting devices for use primarily in lightwave transmission systems.
The very wide transmission window from about 0.8 to 1.6 .mu.m in present low-loss optical fibers permits the use of wavelength multiplexing to increase the transmission capacity of a fiber. Multiple wavelength light emitting devices which operate in this range have previously been disclosed. See, for example, the article entitled "Dual-Wavelength Surface Emitting InGaAsP LEDs," by T. P. Lee, C. A. Burrus and A. G. Dentai, Electron Letters, 16, page 845 (1980) or the article entitled "A Transparent InGaAsP-InP Luminescent Diode for Optical Wavelength Multiplex Operation of Fiber Systems," by W. E. Proebster and H. Grothe, IEEE Transactions Electron Devices, ED-30, page 119 (1983).
The prior art devices are generally monolithic structures. Producing a second wavelength in a monolithic structure usually requires growing two active layers with different bandgaps either in a single growth procedure or a consecutive growth procedure with an intermediate etch step. The former procedure involves complex processing to electrically access the active layers individually while the latter involves a difficult regrowth process.
It has been proposed to provide a multiwavelength light emitting device by using individual LEDs emitting at different wavelengths and coupling them in series using short lengths of optical fiber. (See Proebster and Grothe, "A Transparent InGaAsP-InP Luminescent Diode . . . ," IEEE Transactions Electron Devices, ED-30, page 119 (1983).) While this approach has many advantages, it may also involve costly, complex, multiple LED to fiber alignments.
It is therefore an object of this invention to provide a multiwavelength light emitting device where the light can be coupled effectively into a single optical fiber.